2019-02-08  Jakub Jelinek  <jakub@redhat.com>

	PR c++/88977
	* pt.c (convert_nontype_argument): Pass true as manifestly_const_eval
	to maybe_constant_value calls.

	* g++.dg/cpp2a/is-constant-evaluated7.C: New test.

--- gcc/cp/pt.c.jj	2019-02-05 10:04:19.038028029 +0100
+++ gcc/cp/pt.c	2019-02-08 09:46:23.370257199 +0100
@@ -6821,12 +6821,14 @@ convert_nontype_argument (tree type, tre
 	    /* Make sure we return NULL_TREE only if we have really issued
 	       an error, as described above.  */
 	    return (complain & tf_error) ? NULL_TREE : error_mark_node;
-	  expr = maybe_constant_value (expr);
+	  expr = maybe_constant_value (expr, NULL_TREE,
+				       /*manifestly_const_eval=*/true);
 	  expr = convert_from_reference (expr);
 	}
       else if (TYPE_PTR_OR_PTRMEM_P (type))
 	{
-	  tree folded = maybe_constant_value (expr);
+	  tree folded = maybe_constant_value (expr, NULL_TREE,
+					      /*manifestly_const_eval=*/true);
 	  if (TYPE_PTR_P (type) ? integer_zerop (folded)
 	      : null_member_pointer_value_p (folded))
 	    expr = folded;
--- gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated7.C.jj	2019-02-08 09:53:47.255935430 +0100
+++ gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated7.C	2019-02-08 09:49:45.159957823 +0100
@@ -0,0 +1,18 @@
+// P0595R2
+// PR c++/88977
+// { dg-do compile { target c++11 } }
+
+namespace std {
+  constexpr inline bool
+  is_constant_evaluated () noexcept
+  {
+    return __builtin_is_constant_evaluated ();
+  }
+}
+
+template<bool B> constexpr bool foo () { return B; }
+
+constexpr bool x = foo<std::is_constant_evaluated ()> ();
+constexpr bool y = foo<__builtin_is_constant_evaluated ()> ();
+static_assert (x, "");
+static_assert (y, "");